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Key to Thelypteridaceae

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1 Leaf blades 7-25 (-30) cm long, triangular, < 2× as long as wide (or lanceolate and > 4× as long as wide in the rarely naturalized P. decursive-pinnata); rachis with adnate wings between the pinnae; sori without indusia; midribs of pinnae lacking an adaxial groove; [subfamily Phegopteridoideae]; [Phegopteroid clade]
1 Leaf blades (15-) 20-100 cm long, lanceolate, oblong-lanceolate, or triangular, > 2× as long as wide; rachis without adnate wings between the pinnae; sori with reniform indusia; midribs of pinnae with an adaxial groove (adaxial groove lacking in Macrothelypteris).
..2 Midribs of the pinnae lacking an adaxial groove; leaf bipinnate to tripinnate; [subfamily Phegopteridoideae]; [Phegopteroid clade]
..2 Midribs of the pinnae with an adaxial groove; leaf pinnate to pinnate-pinnatifid; [subfamily Thelypteridoideae.
....3 Leaves 1-pinnate (the pinnae entire or serrate, and also often undulate); veins forming parallel rows of more than 5 areoles between the pinna margin and the main vein, the areoles with a single excurrent, free veinlet; sori elongate; [Goniopteroid clade]
....3 Leaves 1-pinnate-pinnatifid (the pinnae lobed to pinnatifid); veins all free or at most with a single areole between the sinus and the main vein; sori round or reniform (elongate in Leptogramma).
......4 Stellate hairs present on rachis, veins, and upper leaf blade surface; [n. FL south to s. FL]; [Goniopteroid clade]
......4 Stellate hairs absent; [collectively widespread].
........5 Sori elongate; sporangia with hairs 0.1-0.2 mm long; [endemic to nc. AL]; [Stegnogrammoid clade]
........5 Sori round or slightly longer than wide; sporangia glabrous; [collectively widespread].
..........6 Basal veins from adjacent lobes of the pinna not meeting at all; lowermost pinnae pinnae of a leaf either as long as the pinnae above (or only slightly smaller), or strongly reduced (with an obvious and strong taper of the blade outline towards the base).
............ 7 Lowermost pinnae of a leaf strongly reduced, at least 3 or 4 pairs distinctly smaller than the longest pair on a leaf (and therefore with an obvious and strong taper of the blade outline towards the base); [Amauropeltoid clade].
............ 7 Lowermost pinnae of a leaf as long as the pinnae above, or only slightly smaller (> 80% as long).
............ ..8 Veins of the pinna-lobes unbranched; lower leaf surface with sessile, reddish, resinous glands; lower surface of costae lacking scales; [montane w. NC and e. TN northeastwards]; [Amauropeltoid clade]
............ ..8 Veins of the pinna-lobes mostly Y-forked; lower leaf surface lacking glands; lower surface of costae with persistent ovate scales; [widespread in our region]; [Thelypteroid clade].
..........6 Basal veins from adjacent lobes of the pinna either uniting either below the sinus (between the sinus and the costa) and therefore forming a united vein continuing to the sinus, or reaching the sinus at the same point; lowermost pinnae of a leaf as long as the pinnae above, or only slightly smaller (> 80% as long) (except in Christella); pinnae 3.5-45 cm long, usually at least the longer > 15 cm long (except in Christella).
............ ....9 Basal veins from adjacent lobes of the pinna either uniting either below the sinus (between the sinus and the costa) and therefore forming a united vein continuing to the sinus; rhizomes 3-12 mm in diameter
............ ......10 Lower leaf surface with sessile, opaque, sulphur-colored or pale yellow glands (obvious without magnification); [Sphaerostephanoid clade]
............ ......10 Lower leaf surface lacking sessile glands (sometimes short-stipitate light yellowish glands present)
............ ....9 Basal veins from adjacent lobes of the pinna reaching the sinus at the same point (but not uniting to form a united vein to the sinus); rhizomes 3-6 mm in diameter.
............ ........11 Lowermost pinnae reduced, smaller than some of those above; costae abaxially lacking scales; blades abaxially lacking glands or with short-stipitate, light yellow or orangish glands; rhizomes relatively short-creeping, brown, scaly; ]Pseudocyclosoroid clade]
............ ........11 Lowermost pinnae the longest or nearly so; costae abaxially with ovate scales; blades abaxially with sessile orangish or reddish, hemispherical glands; rhizomes very long-creeping, blackish, nearly naked; [Goniopteroid clade]
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